Composition and process for displacement plating of zinc surfaces

ABSTRACT

Disclosed is an improved composition and process for the heavy metal displacement plating of a zinc surface. The improved process provides for contacting the zinc surface with a solution containing at least one soluble stabilizing compound containing antimony, tin, copper, lead, germanium, vanadium, arsenic or tungsten. This contact may be effected either by pretreating the metal surface prior to displacement plating or by including the stabilizing compound in the displacement solution itself. The composition is an aqueous one containing both a heavy metal ion and the stabilizing compound. The disclosed process improves the displacement plating composition&#39;&#39;s resistance to degradation and consequent loss of efficiency.

United States Patent Shinomiya et al.

[ Dec. 30, 1975 COMPOSITION AND PROCESS FOR DISPLACEMENT PLATING OF ZINC SURFACES Inventors: Hiroshi Shinomiya, Yokohama;

Kajuro Muro, Komae; Sumio Sakata, Kobe; Shigeki Saida, Tokyo; Seichiro Umehara, Tokyo; Yutaka Tsuchiya, Tokyo; Kunijo Yashiro; Yoshio Moriya, both of Yokohama, all of Japan Assignee: Oxy Metal Industries Corporation,

Warren, Mich.

Filed: Nov. 2, 1973 Appl. No.: 412,120

Foreign Application Priority Data Nov. 6, 1972 Japan... 47-110257 Jan. 11, 1973 Japan 48-5519 US. Cl. 427/421; 106/1; 427/328; 427/383; 427/405; 427/436 1111. c1. C23C 3/00 Field of Search 106/1; l48/6.14 R; 117/130 R, 50; 427/436, 421, 328, 383, 405

References Cited UNITED STATES PATENTS 2/1960 Morse 117/130 R X 3,202,529 8/1965 Dunlap 117/50 X 3,444,007 5/1969 Maurer et al. l48/6.l4 X 3,468,724 9/1969 Reinhold 1 17/130 R X 3,539,403 11/1970 Ries l48/6.l4 3,672,964 6/1972 Bellis 117/50 X OTHER PUBLICATIONS Saubestre, Electroless Plating Today, Aug. 1962, pp. 46-48.

Primary Examiner-Ralph S. Kendall Assistant ExaminerJohn D. Smith Attorney, Agent, or Firm-Arthur E. Kluegel; Richard P. Mueller; Bertram F. Claeboe [57] ABSTRACT Disclosed is an improved composition and process for the heavy metal displacement plating of a zinc surface. The improved process provides for contacting the zinc surface with a solution containing at least one soluble 2 Claims, No Drawings COMPOSITION AND PROCESS FOR 1 DISPLACEMENT PLATING OF ZINC SURFACES BACKGROUND OF THE INVENTION This invention relates to a composition and process for forming a coating on the surface of zinc or alloy thereof by contacting said surface with an acidic solution for displacement plating. It is an object of this invention to render such solutions less sensitive to zinc ion content thereby prolonging their useful life and improving the process efficiency. It is another object of this invention to provide an undercoating for paint having excellent adhesion characteristics.

Conventional processes for treating the surface of zinc or its alloys include displacement plating, chemical plating and chemical conversion coating processes such as chromating and sulfiding with black sulfides. The undercoatings produced by these conventional techniques have not'been entirely satisfactory from the standpoint of corrosion and heat resistance or adhesion characteristics. Further in the acidic displacement plating processes, zinc ions are produced by the treated surface which gradually contaminate the solution, and thus, the initial efficiency for the plating cannot be maintained for a long period of time unless the spent solution is discarded and a fresh solution is supplied. Noticeable degradation of product quality occurs at zinc ion concentrations of 5 g/l and lower. It has now been found that a desensitized acidic solution for displacement platingcontaining nickel, iron or cobalt, suitable for forming a coating on the surface of zinc or an alloy thereof may be obtained by adding to the solution one or more soluble compounds of a desensitizing metal selected from antimony, tin, copper, lead, germanium, vanadium, arsenic and tungsten. It has also been found that the displacement solution may be rendered less sensitive to zinc ion content by contacting'the zinc surface with a solution of one of the foregoing metals' simultaneously with or prior to the displacement plating. Accordingly, this invention includes an acidic solution for'the displacement plating in which a solution containing ionic nickel, iron, or cobalt, is adjusted to the desired pH by adding inorganic and/or organic acids and including a desensitizing metal compound and, if desired, a complexing agent. According to the method, the desensitizing .metal compound may alternatively be employed in a pre-displacementplating treatment. Suitable heavy metal'compounds of nickel, cobalt, and iron include the'inorganic chlorides, sulfates, nitrates and carbonates and organic salts such as the acetates and citrates. Normally, the compound of heavy metal is contained in an amount more than 0.1 g/l, preferably in the range of from 0.1 to SO'g/l calculated as the metal.

Suitable desensitizing metal compounds include stannous chloride, tin borofluoride, stannous acetate, cupric chloride, cupric sulfate, copper citrate, lead chloride, lead nitrate, lead acetate, germanium chloride, germanium oxide, ammonium metavanadate, sodium arsenate, sodium hydrogen arsenate, ammonium magnesium arsenate, ammonium tungstate, sodium tungstate, potassium tungstate, potassium antimony tartrate, potassium antimony oxalate, sodium tetrachloro antimonate and antimony chloride. Such compounds are added to the pretreating solution or the solution for displacement plating in a total amount ranging from 0.001 to 50 g/l calculated as the metal and desirably between 0.01 and 10 g/l. Since no effect can be achieved in an amount less than 0.001 g/l, and no proportional increase can be expected in the efficiency correspondingly to an amount more than 50 g/l, such amounts are economically disadvantageous. When the compounds are to be added to a pretreating solution, they may conveniently be added to the immediately preceding rinsing step or the pickling step.

Supplemental additives for the displacement solution include buffering compounds and a complexing agent for the metallic ions present in the solution or formed by the dissolution. These compounds include tartaric, citric, malic, oxalic, succinic acids and the like and the salts thereof. The amount to be added cannot be standarized depending on the purpose, but generally they are used in an amount ranging from 0.1 to 50 g/l.

In order to adjust the displacement plating solution to a desired pH value, organic or inorganic acids may be used. The inorganic acids include, for example, hydrochloric, sulfuric, hydrofluoric, and fluorosilicic, and the organic acids include citric, acetic, and oxalic. Normally, the acid will be present in an amount ranging from -l to 150 g/l. If the desired pH can be obtained, a

. salt of such inorganic or organic acids may be used. For

example, salts of a heavy metal such as iron, nickel, or cobalt, may be used.

The pH of the solution is generally maintained at a value less than 7 and preferably 1 to 4.5. The process of this invention comprises contacting the surface of zinc or an alloy thereof at a temperature ranging from room temperature to the boiling point of the solution for a sufficient length of time to obtain the desired coating by means of spraying, immersing or brushing, preferably by immersing or spraying for the case where the coating is to be used as an undercoating for painting. In a continuous process for forming a coating in a short period of time, it is desirable to treat the article with the solution at a temperature from 40 to 90C for 2 to 6 seconds. While a satisfactory coating for use as an undercoating for paint can be obtained at a treating temperature of from 50 to C for 3-30 seconds, it can be obtained in a shorter period of time with a higher concentration of the metallic ion and at higher treating temperatures. It takes somewhat longer time for the immersing process than that.for the spraying process, but if an auxiliary means is adopted for stirring the solution or causing it to flow, the coating time is almost the same as that for the spraying process.

The coating treatment of this invention may be best effected by combining it with certain pretreating steps and after treating steps. The pretreating steps comprise steps for degreasing etching by an acid .or alkali solution, surface conditioning, and washing with water subsequent to each treating step. The degreasing step is employed when articles to be surface treated are processed in the presence of oil. The pickling step activates the surface of articles to be treated and strengthens the effect achieved by the main plating treatment. As an after treatment, it is preferable to rinse the formed coating with a dilute aqueous solution of chromic acid. The coating may then be rinsed with water and followed by drying. The coating then is ready for applying paints or other overcoatings. Both the pretreatments and after treatments referred to hereinbefore are normally effected for several seconds to 30 seconds.

The process of this invention is adapted for surfaces of zinc or its alloys including electrogalvanized and 3 hot-dip galvanized steel. By virtue of the treatment with a desensitizing metal compound, it is possible to maintain the initial efficiency for extended periods by inhibiting the deleterious effects normally caused by the increase in the amount of zinc ion dissolved in the plating solution. The coating obtained according to this invention has an excellent adhesion with paints as compared with phosphate coatings, complex coatings based on oxides and chromating coatings.

This invention will be further illustrated by means of the following examples.

EXAMPLE 1 to 3 The adhesion of a film on galvanized steel after having been treated with the acidic solution for displacement plating according to this invention was compared with the film obtained from a conventional acidic solution for displacement plating. Specimens were samples from non-chromating galvanized steel plate 0.27 X 50 X 100 mm having a zinc content of 183 grams/m The specimens were treated in a weak alkaline degreasing agent (Finecleaner, Type 315 prepared by Nihon Parkerizing Co., Ltd.) in a concentration of 20 g/l at 60C for 10 seconds and any trace of the residual degreasing agent was removed by rinsing with water. Then the specimens were pickled in hydrochloric acid at 25C for 5 seconds followed by rinsing with water again. The thus treated specimens were then subjected to displacement for plating using the compositions indicated at 60C for 5 seconds. Then, the specimens were treated in a dilute chromic acid (Percolene" Type 62 prepared by Nihon Parkerizing Co. Ltd.) in a concentration of 20 g/l, followed by removing excess chromic acid solution by squeezing them between rolls and finally drying by means of hot air at 105C. The treatments were all effected by immersion.

Composition of the Displacement Plating Solution The solution was prepared by dissolving nickel carbonate (16- grams), hydrochloric acid (35% 30 grams), hydrofluoric acid (55% 3 grams) and citric acid (5 grams) in city water 1 liter. Since the solution was reused repeatedly after the preparation, the components were constantly replenished in order to maintain the composition constant. Zinc was gradually dissolved into the solution from the surface treated and eventually reached a concentration of about 50 g/l. All of the examples and controls contained 65 g/l chloride, 1.6 g/l fluoride, 5 g/l citric acid and were adjusted to a pH of 2. In separate tests, desensitizing metal compounds were added as follows: sodium hydrogen arsenate (2.1 g/l); stannous chloride (0.96 g/l); germanium chloride (1.5 g/l). The compositions are summarized in Table I, excluding the Cl, F and Citric acid.

results of adhesion test on the coated film effected after the baking.

Control specimens were also prepared from the same hot galvanized steel plate, plated with nickel, painted under the same conditions except that the solution contained no zinc ion in Control No. l and no arsenic nor stannous nor germanium ion in Control No. 2 and the adhesion of the coated film was tested. Table I shows also results of these controls.

Testing Procedure for the Adhesion of Coated Paint Film on the Metallic Surface (Bending Test) After the coating of paint, the specimens were allowed to stand at 25C for 24 hours. They were then folded 180. The folded portion was pressed by means of a vise. Scotch tape was applied to the folded surface and was peeled off quickly after 1 minute from the application.

After the test, the specimens were evaluated according to the percentage of peeled area on the folded surface. When the specimens were pressed together by means of the vise, the testing condition can be modified from the severe to moderate ones by inserting a desired number of plates having the same thickness as that of specimens between the confronted surfaces of folded specimens. Corresponding to the number of plates inserted therebetween, the test results were designated as l T when one plate thickness was inserted, as 2 T when two plates were inserted and as 0 T when no plate was inserted therebetween. Accordingly, the smaller the number of the inserted plates was, the more severe the test condition becomes. Each test was repeated for 5 specimens and the average is reported.

The results were then classified in accordance with the following scale:

5 No peeling or cracking of the film.

4 Less than 1% peel.

3 225% peel.

2 26-50% peel.

1 In excess of 50% peel.

EXAMPLES 4 to 6 Additional specimens were plated with nickel under the same conditions as those disclosed in Example 1 except that sodium tungstate (0.9 g/l), copper citrate (1.4 g/l), and lead chloride (0.65 g/l) were used as desensitizing metal compounds. The principal solution components are shown in Table 11. The specimens were thereafter undercoated with vinyl-modified epoxy paint and baked at 275C for 40 seconds, followed by overcoating with a thermosetting acrylic paint to a total thickness of the coated film of 15 microns and baking at 275C for seconds. The coated specimens were tested in the same manner as disclosed in Example 1.

TABLE 1 Composition Ni Zn As Sn Ge Z-TBcnd Example 3 8 50 0.5 3.4 Control No. l 8 4.2 Control No. 2 8 51) l.()

The surface treated specimens were then coated with a polyester paint to a thickness of 12 microns and baked at 275C for 90 seconds. Table 1 also shows the Table 11 shows the results obtained. In the case of lead chloride, the solution was further added with DETA 2Na.2H O (1.35 g/l) in order to enhance the dissolution thereof.

Controls were prepared by plating nickel in the similar manner as disclosed in Controls 1 and 2 except that 315 prepared by Nihon Parkerizing Co. Ltd.) in a concentration of g/l at 60C for 3 seconds and any trace of the residual degreasing agent was removed by rinsing with water. Then the specimens were pickled in 5% the coatings were applied under the same conditions as 5 hydrochloric acid at C for 5 seconds, followed by in these examples and tested in the same manner as rinsing with water again. The specimens were then disclosed in Example 1 to 3. Table II shows also these treated with a surface conditioning agent having the results for the controls. following composition at 25C for 5 seconds. Immedi- TABLE 11 Composition O-T Bend i Zn W" CU2+ Pb Average of Example 5 Panels 4 8 all all 9!! 11Il I71! 5 8 50 0.5 3.8 6 8 50 0.5 3.6 Controls 3 8 4.0 Controls 4 8 50 1.4

ately after the conditioning the specimens were treated 20 EXAMPLES 7 9 with a displacement plating solution having the.same Specimens were prepared by coating with nickel and composition as'disclosed in Control 2 at 60C for 5 coated with the paint and baked under the same condiseconds. After the plating treatment, any trace of the tions as those disclosed in Example 1 except that amresidual plating solution was removed by rinsing with monium meta-vanadate (1.75 g/l) or stannous chloride water. After the treatment with dilute chromic acid (0.95 g/l) or copper citrate (1.4 g/l) was used as the (Percolene, Type 62 prepared by Nihon Parkerizing desensitizing metal compounds, and all ofcoating oper- Co. Ltd.) in a concentration of 20 g/l, the specimens ations were conducted by spraying. Table III shows the were squeezed between rolls to remove any excess of results of the adhesion test. the residual chromic acid and dried with hot air at Controls were prepared by plating nickel in the simi- 105C. The treatments were all conducted by spraying lar manner disclosed in Controls in Examples 1 to 3 to complete the nickel plating. The specimens were except that the coatings were applied under the same then coated with a paint under the completely same conditions as in these examples and tested in the same treating conditions as disclosed in Example 4 to 6. manner as disclosed in Examples 1 to 3. Table III shows Table IV shows the results obtained on the adhesion also these results for the controls. test.

TABLE III Composition Ni Zn V Sn Cu 2 -T Bend Average of 5 Panels '7 8 0! 50 ll 05 0!! all all 4 8 8 50 0.5 5.0 9 8 50 0.5 4.0 Control 5 8 Control 6 8 50 2.0

TABLE IV Composition O-T Bend Sn WH Na Cl Citric pH Average of Example Acid 5 Panels 0 2 all a!! nll 13 all 19 nil 2 40 Control 7 Without any surface conditioning 2.0

EXAMPLES 10 to 11 EXAMPLE 12 These examples show effects obtained in the cases where the article has been pretreated with a solution containing stannous ion or a tungstate as a surface conditioning agent by spraying immediately before the known conventional plating treatment. The stannous ion was added as stannous chloride and the tungsten as sodium tungstate.

Specimens were sampled from non-chromating galvanized steel plate (0.27 X X 100 mm) having a zinc content of 183 grams/m-. The specimens were treated in a weak alkaline degreasing agent (Finecleaner, Type This example shows an embodiment in which specimens were treated with a pickling solution containing 50 ammonium metavanadate prior to the conventional treatment for displacement plating.

Specimens were sampled from non-chromated zinc hot-dip galvanized steel plate (0.27 X 50 X mm) having a zinc content of 183 grams/m The specimens were treated with a weak alkaline degreasing agent (Finecleaner, Type prepared by Nihon Parkerizing Co. Ltd.,) in a concentration of 20 g/l at 60C for 3 seconds and any trace of the residual degreasing agent 7 was removed by rinsing with water. They were then pickled in a pickling solution having the following composition at 25C for 5 seconds, followed by rinsing with water. They were subsequently treated with a displacephosphating solution containing 2.4 g/l of Zn, 9 g/l of P 2.5 g/l of N0 2 g/l of Ni and 2 g/l ofF by spraying at 65C for 25 seconds. After the treatment with the zinc base phosphating solution, the specimens were ment plating solution having the same composition as after-treated and coated with paint under the same disclosed in Control 2 at 60C for 5 seconds. After the conditions as those disclosed in Example 13. treatment, they were rinsed with water to remove the residual solution. The specimens were then treated Salt Spraymg Test with dilute chromic acid (Percolene, Type 62 prepared This is a corrosion test according to which specimens by Nihon Parkerizmg Co. Ltd.) in a concentration of are sprayed with 5% saline solution. The specimens g/l and they were squeezed between rolls to remove have been scratched diagonally from one corner to the residual chromic acid and dried with hot air at another by means of a thin-bladed knife immediately 105C. The treatments were all conducted by spraying before the test. After the test, the width of blisters to complete the nickel coating. The specimens were formed along the scratch is measured and represented then coated with a paint under the same painting condi- 15 as a distance in mm perpendicular to the scratch. The trons as disclosed in Example 4 to 6. Table 5 shows the smaller the salt spray value, the better the corrosion results of adhesion test on the thus-treated surface. resistance is.

TABLE V Composition Citric O-T Bend HCl V1+ NH, Acid pH Average of Example 5 Panels [2 [0 I7 I all 02 all 6 all 1 0 Control 8 50 2.0

EXAMPLE 13 Each test is repeated with 5 specimens and the aver- Panels were treated as in Examples 1-3 using 0.3 g/l age reported of antimony added as potassium antimony tartrate as TABLE the desensitizer. The adhesion was tested for displace- Article prepared Comm treated ment plating solution having zinc ion contents of 0, 25, with Zinc and 50 g/l. For comparison, results were also obtained fi gf s' g g'fiffjff using an antimony-free plating solution.

Bend Test TABLE VI GT 4.8 1.4 lT 5.0 2.6 Quantity of Zinc 2-T Bend Average 2T 5.0 3.6

dissolved in the of 5 Panels Salt Spray Test plating solution With Antimony Control 366 hrs. 0 0.5 l.0 mm

0 I g/l 5 4.4 40 25 g/l 4.8 2.4 50 g/l 5 1.6

EXAMPLE 15 The adhesion of painted film was tested for an article EXAMPLE 14 treated with an acid1c so lut1on for the displacement plating according to this invention as compared with In thls example, the adhslon and that for an article treated with a conventional acidic tance were tested for the painted coating on an article solution f the displacement plating, ft aging f treated with a displacement plating solution formulated both acidic solutions according to this invention as compared with that of Specimens were sampled from the Same hot b the P F coatmg the Same yp of artlcle nized steel plate, plated with iron under the same contfeated Wlth a Convemlonal Zmc base P P S SQIu' ditions as disclosed in Example 13 except that the distlonplacement plating solution was replaced by that having sPec1men5 were Sampled f Same hot galva' the following composition and subjected to the same q Steel P and P wlth mckel under the same adhesion test of painted film as disclosed in said examconditlons as disclosed in Example 13 except that po- PIC. The results are Shown in Table v 1 tassium antimonyl tartrate in the displacement plating solution was used in an amount of 0.274 grams (0.1 Ferric oxide 15 grams grams calculated as metallic antimony). Table VII 5% Hydrochloric acid 141 grams shows results of the adhesion test (conducted in the 5 YQ W field 3 grams l t t Citric acid 5 grams Same manner as m Example 13) i the t SRray Potassium antimonyl tartrate 0.2 grams (0.073 grams Controls were prepared by treating the specimens in calculated as metallic antimony) an alkaline degreasing agent at 60C for 10 seconds, PH 2 followed by rinsing with cold water. The specimens were then pickled with 5% hydrochloric acid for 3 Controls were prepared by sampling from the same seconds, followed by rinsing with water. The specimens were subsequently treated with a solution containing surface conditioner in a concentration of 3 g/l by spraying at 40C for 3 seconds and then with a zinc base hot galvanized steel plate and plating with iron under the same conditions as disclosed in the Example except that potassium antimonyl tartrate was eliminated from the displacement plating solution.

TABLE VIII Zn amount dissolved in Article pretreated In this example, the adhesion of painted film was tested for an article in which an antimony compound was added to the solution for a pretreating step, i.e., for the rinsing step with water immediately before the displacement plating step in comparison with that for an article pretreated with a solution containing no antimony compound.

Specimens were sampled from the same hot galvanized steel plate, plated with nickel by employing the same displacement plating solution without any antimony compound as disclosed'in Control in Example 13 except that after the pickling and rinsing with water, the surface to be treated was sprayed with an aqueous solution of potassium antimonyl tartrate in a concentration of 22 g/l (8 g/l calculated as antimony) as a surface conditioner at room temperatures for seconds and coated with a paint. The adhesion test was conducted in the same manner as disclosed hereinbefore. Table IX shows the results obtained.

Controls were prepared by plating with nickel and coated with a paint in the same manner as disclosed in Example 15 except the absence of said surface treatment with the solution containing an antimony compound.

EXAMPLE 17 In this example, the adhesion of painted film was tested for an article in which an antimony compound 5 was added to the pickling solution in comparison with that for a substrate pretreated with a conventional pickling solution.

Specimens were sampled from the same hot galvanized steel plate as disclosed hereinbefore, plated with nickel by employing the same displacement plating solution containing no antimony compound as disclosed in Control for Example 13 and coated with a paint in the same manner as disclosed in Example 13 except that the article was sprayed with a pickling solution containing 5 g/l of tartric acid and 3 g/l of potassium antimonyl tartrate beside other ingredients at room temperature for 3 seconds. The results obtained are shown in Table X. The table shows also the results of the Control in which the substrate was treated in the same manner as disclosed immediately before except that the pickling solution is replaced by 5% HCL solution.

TABLE X Zn content dissolved Article retreated What is claimed is:

1. A process for providing a paint base coating on a zinc or zinc alloy surface, comprising contacting said surface with an aqueous acidic composition suitable for the displacement plating of a zinc or zinc alloy surface, consisting essentially of a. a soluble heavy metal compound selected from the group consisting of nickel, cobalt and iron in an amount of 0.1 50 g/l expressed as the heavy metal; and

b. a soluble compound of a desensitizing metal selected from the group consisting of antimony, tin, copper, lead, germanium, vanadium, arsenic and tungsten in an amount of at least 0.001 g/l expressed as the metal.

2. The process of claim 1 wherein said contact is effected by the immersion or spray technique. 

1. A PROCESS FOR PROVIDING A PAING BASE COATING ON A ZINC OR ZINC ALLOY SURFACE, COMPRISING CONTACTING SAID SURFACE WITH AN AQUEOUS ACIDIC COMPOSITION SUITABLE FOR THE DISPLACEMENT PLATING OF A ZINC OR ZINC ALLOY SURFACE, CONSISTING ESSENTIALLY OF A. A SOLUBLE HEAVY METAL COMPOUND SELECTED FROM THE GROUP CONSISTING OF NICKEL, COBALT AND IRON IN AN AMOUNT OF 0.1 - 50 G/L EXPRESSED AS THE HEAVY METAL; AND B. A SOLUBLE COMPOUND OF A DESENSTITZING METAL SELECTED FROM THE GROUP CONSISTING OF ANTIMONY, TIN, COPPER, LEAD, GERMANIUM, VANADIUM, ARSENIC AND TUNGSTEN IN AN AMOUNT OF AT LEAST 0.001 G/L EXPRESSED AS THE METAL.
 2. The process of claim 1 wherein said contact is effected by the immersion or spray technique. 